Forces Acting on the Aircraft Structure

An aircraft is subject to various forces which act on the structure both on the ground and in Flight.

During flight the wings produce lift which tends to bend the wing upwards, as a result there will be compression on the upper surface and tension on the lower. Lift also causes a torsional force which twists the wing.

An aircraft flying straight and level at a constant speed will be subject to 1g. Any change in attitude will change the g which in turn alters the weight of the structure and the loads.

Load Factor is the ratio of the lift of an aircraft to its weight and represents a global measure of the stress "Load" to which the structure of the aircraft is subjected:

• n = L / W ,

where:

n: Load Factor

L: Lift

W: Weight

During level flight weight at a given time is constant and cannot be changed. The only component that can be changed instantaneously is lift. This can be done by an upward gust which will force the aeroplane to gain height. This upwards force is added to lift produced by the aeroplane's wings causing the Load Factor to increase. If this happens when flying with high speed or exceeding the manoeuvering speed, lift gets higher and bending forces at wings also get extremely high.

The fuselage structure may be damaged by exceeding the manoeuvring speed in heavy gusts.